A typical magnetoresistive (MR) read head includes an MR read sensor, which is located between first and second shield layers. The first and second shield layers act as leads for the sensor. Thus, the lead/shield layers are connected to the read sensor for conducting a sense current therethrough. When the read sensor is subjected to positive and negative signal fields from tracks on a rotating magnetic disk in a disk drive the resistance of the read sensor changes. These resistance changes cause potential changes in the sense current circuit, which are processed as playback signals by processing circuitry.
The read head has an exterior head surface that faces the rotating magnetic disk and is supported on swirling air from the rotating disk, which is referred to as an air bearing. For this reason the head surface is referred to as an air bearing surface (ABS).
The read sensor has a back edge that is recessed in the read head opposite the air bearing surface. The back edge is precisely located by photolithography processing. During construction the ABS must also be precisely defined so that the read sensor has a precise stripe height, which is the distance between the ABS and the back edge. This is accomplished by lapping (grinding) a wafer on which the MR head is constructed until the ABS is achieved.
The stripe height of MR sensor is determined by lapping the head structure while measuring the resistance of an electrical element. This electrical element is called an electronic lapping guide (ELG). The back edge of the ELG is formed in the same photo and subtractive processes as the back edge of the sensor element, i.e. the ELG back edge and the sensor back edge are self-referenced to each other.
One problem with the present ELG strategy occurs when smaller sensor heights are required. For proper lapping to the target stripe height, a final predetermined ELG resistance based on the sheet resistance of the material is required. As the target stripe heights decrease, the final ELG resistance is made greater. This increase in final resistance will invariably require modification of lapping algorithms and electronics to sense the higher resistance. Although the geometry of the lapping guide can be changed to reduce the final resistance, i.e. decrease the ELG length or offset the back edge of the ELG relative to the sensor element, the lapping precision is degraded since the rate of resistance change versus ELG height is also reduced by these changes.
A second problem associated with electronic lapping guides occurs when new sensor materials with higher magnetoresistance, DR/R characteristics are used. When the ELG is formed using this sensor material, the sheet resistance, Rs, of the ELG material can vary depending on the orientation of the magnetization of the free and pinned layers. These orientations can be perturbed by external fields or by stress induced by the lapping process. Such an Rs change can affect final stripe height independent of the lapping algorithm precision.
A third problem associated with electronic lapping guides occurs when “current perpendicular to the plane” (CPP) structures are used, such as tunnel valve sensors. The sheet resistance of such structures as measured across the planes is typically low, thereby making the resistance of the ELG too low for accurate measurements of resistance changes during lapping. This reduces final ELG resistances to values on the order of 2 to 4 ohms. This is particularly so for tunnel valve structures where the sensor consists of capping layers composed of noble metals (e.g., Pt, Pd, Rh, Au, Cu).
A so-called mill-refill process has been used to replace the sensor material with other thin-film materials in order to tailor the resistivity of the electronic lapping guide. The mill-refill process requires that the electronic lapping guide material have a maximum “effective milling thickness” that is completely milled when the sensor is completely milled.
In order to make high areal density heads, partially milled sensor structures have been considered. A partially milled sensor structures involves defining the stripe-height by partially milling the sensor. To produce a partial mill structure, electronic lapping guide material must be created independently of the sensor material. The purpose is to not only tailoring the resistance, but also to assure that the edges of the electronic lapping guide are completely milled at the termination of the sensor's partial mill. However, using tunneling magnetoresistance (TMR) materials for electronic lapping guides would guarantee that the electronic lapping guides are shorted for a partial mill.
Two actions are required to implement the partial mill process. First, the material in the ELG region that will fully mill when the element is only partially milled must be placed. Next, the sensor must be cleared in the field in a step independent of that which performs the sensor mill.
Two separate photolithography steps during the partial mill have been used to meet the two requirements indicated above. First, the sensor is deposited full film. Then, the sensor film around just the electronic lapping guide is milled and replaced with a predetermined electronic lapping guide material. The sensor film in the field is milled and replaced with alumina. The back edge of the strip is then defined with a partial mill simultaneously with the back edge of the electronic lapping guide.
If the number of manufacturing steps could be reduced, the cycle time and cost of manufacturing the sensor could be reduced. In addition, using the above process results in the electronic lapping guide not being in the same focal plane as the element, thereby making the electronic lapping guide edge to sensor-edge sensitive to variations in focus.
It can be seen that there is a need for a method for merging sensor field-mill and electronic lapping guide material placement for a partial mill process and sensor formed according to the method.